NEW YORK, Mar 07 (Reuters Health) -- In a new and unique approach to
fighting AIDS, researchers have created an experimental HIV vaccine using a
weakened strain of the rabies virus.
So far, the vaccine appears to elicit a strong immune response in mice but
it is not clear if the vaccine would be safe or effective in humans, according
to researchers from Thomas Jefferson University in Philadelphia, Pennsylvania.
Although the approach may not work in humans, the researchers remain "cautiously
optimistic," said senior investigator Dr. Roger J. Pomerantz.
In a new study, Pomerantz and colleagues genetically engineered a weakened
strain of rabies virus, which is used in vaccines and cannot cause rabies, to
produce HIV proteins. The rabies virus strain is approved for use in animal
vaccines but not for use in humans.
When mice were injected with the modified virus, they produced a strong
immune response against the HIV proteins.
The mice not only produced antibodies (which are elicited by most vaccines),
they also produced killer T cells that recognized HIV. Because antibodies are
generally inadequate to protect against HIV, the theory is that a successful
vaccine must also generate such killer T cells.
The findings, which will be published in the March 28th issue of the
Proceedings of the National Academy of Sciences, were released prior to
publication.
Other approaches to HIV vaccines rely on using killed HIV to stimulate an
immune response.
"Whether or not it works in humans, this is a rationally designed approach,"
Pomerantz told Reuters Health, "as opposed to one where you just throw dead
virus into a vaccine because it worked well for something like polio."
This approach is also safer than some other vaccine designs. "If you use a
live, attenuated HIV, you may get a very good vaccine, but very few people would
want to use it in humans because of the obvious safety risk," he explained.
Rabies virus does not interfere with the production of proteins like other
viruses used in vaccines. It is slow to replicate, "which may be good to express
HIV antigen longer. And it doesn't kill cells, which is important," said lead
author Dr. Matthias Schnell. The researchers will continue to analyze the immune
response in mice so they can come up with the best virus, which will then be
used in rhesus monkeys, he said.
The finding "shows there are novel approaches, rather than just using killed
viruses or subunit vaccines, that may make more sense pathophysiologically for
this particular disease," Pomerantz told Reuters Health.
"This is the first demonstration of the potential usefulness of an entirely
different line of viruses, a group called nonsegmented RNA viruses, of which
rabies is only one," he said. "Although we think (rabies) has the best molecular
characteristics to make it a reasonable vaccine approach... a variety of other
related viruses may also be used in vaccine development."
